Method for the electrolytic decomposition of titanium tetrachloride



Dec. 4, 1962 Filed July 28. 1960 G. TRUMPLER METHOD FOR THE ELECTROLYTIC DECOMPOSITION OF TITANIUM TETRACHLORIDE 4 Sheets-Sheet l Jnvemor: a g I (A M 581440 Dec. 4, 1962 Filed July 28, 1960 G. TRUMPLER 3,067,112 METHOD FOR THE ELECTROLYTIC DECOMPOSITION 0F TITANIUM TETRACHLORIDE 4 Sheets-Sheet 2 JnIren for:

" Wsm Dec. 1962 G. TRUMPLER 3,067,112

METHOD FOR THE ELECTROLYTIC DECOMPOSITION OF TITANIUM TETRACHLORIDE Filed July 28, 1960 4 Sheets-Sheet 3 Jnvenfor;

Dec. 4, 1962 G. TRUMPLER 3,067,112

METHOD FOR THE ELECTROLYTIC DECOMPOSITION 0F TITANIUM TETRACHLORIDE Filed July 28, 1960 4 Sheets-Sheet 4 Tit/4 Jnvenfor:

N W m United States Patent 3,067,112 METHOD FUR THE ELEQTROLYTIC DECUMPQSK- TIGN 0F TITANIUM TETRACHLQRiDE Gottfried Triimpler, Zurich, Switzerland, assignor to Lonza Chemical and Electrical Works Limited, Gampel,

Wallis, witzerland Filed July 28, 1969, Ser. No. 45,898 Claims priority, application Switzerland July 31, 1959 18 Claims. (til. Zita-61) The present invention relates to a method and apparatus for the electrolytic decomposition of titanium tetrachloride, and more particularly, the present invention is concerned with producing lower titanium chlorides as well as metallic titanium from titanium tetrachloride.

Attempts have been made to produce titanium metal by electrolysis of titanium chloride in such a manner that titanium tetrachloride is introduced into the molten bath consisting of alkali and alkaline earth chlorides and that the titanium tetrachloride dissolved in such bath is then subjected to cathodic reduction. Thereby, the titanium tetrachloride will be reduced in a step-wise manner, first to its triand dichloride. The thus formed lower chlorides of titanium with then be recovered and will be subjected to a second cathodic reduction to metallic titanium. Thus, two separate electrolytic reduction processes must be carried out, the first one for reducing titanium tetrachloride to lower titanium chlorides and the second reduction process for reducing the lower titanium chlorides to metallic titanium. To proceed as outlined above has certain advantages in comparison with attempts to reduce titanium tetrachloride in a single electrolytic reduction process directly to metallic titanium. Such direct reduction of titanium tetrachloride to metallic titanium is a slow and uneconomical process due to the low solubility of titanium tetrachloride in the molt-en chlorides of alkali or alkaline earth metals. On the other hand, the first discussed method requires two separate operations, namely first the reduction of titanium tetrachloride of low concentration to lower titanium chlorides and thereafter the separate process of electrolytically reducing the lower titanium chlorides to metallic titanium. The lower titanium chlorides can be dissolved in much higher concentration in the molten alkali or alkaline earth metal chlorides.

It is therefore an object of the present invention to overcome the above discussed difficulties in the production of titanium and lower titanium chlorides.

It is a further object of the present invention to provide a method according to which metallic titanium and/ or lower titanium chlorides can be produced from titanium tetrachloride in a continuous, simple and economical manner.

=lt is still another object of the present invention to provide an apparatus for the electrolytic decomposition of titanium tetrachloride which will allow the production of lower titanium chloride and/or titanium metal in a continuous manner and requiring only a single electrolytic bath.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention includes a method of reducing gaseous titanium tetrachloride and recovering the products formed by reduction of the titanium tetrachloride, comprising the steps of contacting during spaced first phases a current conducting member with a liquid bath consisting essentially of a solution of a lower titanium chloride in at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, the bath during the first phases being subjected to electrolysis with the current conducting member acting as cathode, and surrounding the current conducting member during the second phases alternating with the first Phases with gaseous titanium tetrachloride, so that during first phases electrolytic reduction of the bath will take place under formation on the member of a layer adapted to reduce gaseous titanium tetrachloride, and during second phases the layer will react with the surrounding titanium tetrachloride reducing the same and forming a layer of reduced titanium tetrachloride on the member, the layer of reduced titanium tetrachloride being dissolved in the bath during the subsequent first phase, and recovering reduced titanium tetrachloride from the bath.

The present invention also contemplates in a device for the decomposition of titanium tetrachloride under formation of reduction products of the same, in combination, electrolytic means for electrolytically producing a reducing agent adapted to reduce gaseous titanium tetrachloride, the means including a current-conducting member acting as cathode adapted to be covered by the reducing agent, container means adapted to contain gaseous titanium tetrachloride, and means for reciprocally moving the current-conducting member between a position wherein the same forms part of the electrolytic means and upon operation of the same will be covered with the reducing agent, and a position wherein the member is located in that container means so that the reducing agent on the member will come in contact with the titanium tetrachloride and will reduce the same.

Thus, according to the method of the present invention, the difiiculties previously experienced in the electrolytic production of lower titanium chlorides and metallic titanium from titanium tetrachloride are overcome by reducing all or at least the major portion of the titanium tetrachloride while the same is in gaseous state and not while the same is dissolved in a suitable electrolytic bath.

The process is carried out according to the present invention, in two phases which alternate with each other, in such a manner that a cathode is alternatingly brought in contact with the electrolyte and with the gaseous titanium tetrachloride or a gaseous mixture including titanium tetrachloride. Thereby, in the first phase, namely while the cathode is in contact with the molten electrolyte, a reducing agent will be formed at the cathode, and this reducing agent which is capable of reducing titanium tetrachloride will then come in contact with the gaseous titanium tetrachloride when the cathode during the second phase is removed from the molten electrolyte and introduced into the gas space which contains titanium tetrachloride. During this second phase, the thin layer of reducing agent which will have formed on the surface of the cathode during the first phase, will chemically react with the surrounding gaseous titanium tetrachloride under reduction of the latter. This twophase operation is continued by alternatingly contacting the molten electrolyte and the gaseous titanium tetrachloride with the current conducting member which serves as a cathode, until the desired quantity of reduction products of titanium tetrachloride has been obtained. In this manner, according to the present invention, the advantage is obtained that the electrolysis of titanium compounds is carried out with much greater concentration of titanium compounds in the molten electrolyte than would be possible if the molten electrolyte would contain only dissolved titanium tetrachloride. According to the present invention, during the second phase of the above described process titanium tetrachloride will be reduced for instance to lower titanium chlorides and during the subsequent first phase of the process, the cathode when being immersed into the electrolyte will carry into the same such lower titanium chlorides which will more easily dissolve in the molten electrolyte, i.e. the molten alkali or alkaline earth metal chloride, than would titanium tetrachloride.

Thus, the method of the present invention can be carried out by electrolysis of an electrolyte consisting of molten alkali and alkaline earth metal chlorides which may or may not contain a small quantity of dissolved titanium tetrachloride. Thereby a reduction product consisting either of alkali or alkaline earth metal or metallic titanium or of a lower titanium chloride will be formed on the cathode. The cathode is then removed from the electrolyte and brought in contact with gaseous titanium tetrachloride. The reducing agent on the cathode, be it alkali or alkaline earth metal or titanium metal or a lower titanium chloride, will then react with the gaseous titanium tetrafluoride under formation of reduction products of the same which may be lower titanium chlorides or, under certain conditions, may also be metallic titanium. The thus formed reduction product of titanium may be recovered prior to reintroduction of the cathode into the electrolytic cell, or such lower titanium chlorides adhering to the cathode may be reintroduced together with the same into the electrolytic cell and the lower titanium chlorides will then be dissolved in the molten electrolyte. The electrolytic cell, preferably includes a diaphragm separating the cathode area from the anode area of the cell. As discussed above, the cell contains at least one cathode which alternatingly is in contact with the molten electrolyte and with a titanium tetrachloride containing gas space, whereby at the effective surface areas of the cathode during the phase while the same is in contact with the molten electrolyte, a reducing agent will be deposited which reducing agent then during the second phase while the cathode is located in the gas space, will react with the gaseous titanium tetrachloride under reduction and formation of lower titanium chlorides of the same. The thus formed lower titanium chlorides are then reintroduced into the molten electrolyte when the cathode during the next following first phase again contacts the molten electrolyte. The lower titanium chloride are then dissolved in the molten electrolyte, so that the concentration of lower titanium chlorides in the molten electrolyte is constantly increased. During operation of the electrolytic cell during successive spaced first phases of the process, the lower titanium chlorides dissolved therein may be further reduced either for instance from titanium trichloride to titanium dichloride or even to metallic titanium so as to form a reducing agent which will adhere to the cathode and which during the subsequent second phase of t. e preferably continu- Ous process will again come in contact with gaseous titanium tetrachloride.

Thus, formation of the reducing agent and reaction of the same with titanium tetrachloride are two phases of the process which alternate with each other and which may be of varying length, i.e. the time required for producing the desired quantity of reducing agent adhering to the cathode may not be equal to the time required for reacting the thus formed reducing agent in the subsequent second phase of the process with gaseous titanium tetrachloride. However, the entire process of the present invention is a unitary process which consists essentially of two alternating steps which are repeated over and over again during the operation of the process.

Whet er the reducing agent which is deposited at the cathode during the operation of the electrolytic cell will consist of an alkali or alkaline earth metal, or of a lower titanium chloride such as titanium dichloride or or" metallic titanium will depend on the cathode potential which can be easily adjusted. It has been found that it is advantageous to form during the initial period of the process and while the concentration of lower titanium chloride in the molten electrolyte is relatively low, a reducing agent which consists of alkali or alkaline earth metal.

However, after the process has been in operation for some time and the concentration of titanium chlorides in the molten electrolyte has sufi'iciently increased, it is preferred to adjust the cathode potential in such a manner that either titanium metal or titanium dichloride will be deposited on the cathode and will subsequently react with the gaseous titanium tetrachloride under reduction of the latter. For deposition of the alkali or alkaline earth metal on the cathode, a higher cathode potential is required than for depositing a titanium-containing reducing agent thereon. Thus, the cathode potential is preferably reduced as soon as the concentration of titanium chlorides in the molten electrolyte has reached a desired minimum level. Thereafter, no more alkali or alkaline earth metals are deposited on the cathode but only titanium metal or lower titanium chlorides which are capable of reducing gaseous titanium tetrachloride.

it is possible to carry out the method of the present invention in such a manner that there will be no contact between the gaseous titanium tetrachloride which is to be reduced and the electrolytic bath consisting of molten alkali and alkaline earth metal chlorides having titanium chlorides dissolved therein. However, it is frequently more convenient to have the titanium tetrachloride containing gas space directly adjacent the molten bath of electrolyte and consequently there will be contact between gaseous titanium tetrachloride and the molten electrolyte. This will lead to the solution of relatively small quantities of titanium tetrachloride in the molten electrolyte and such dissolved titanium tetrachloride will then also participate in the electrolytic reduction and formation of the reducing agent. However, due to the relatively small solubility of titanium tetrachloride in the molten electrolyte, only relativelysmall quantities of titanium tetrachloride will be dissolved and the concentration of the latter in the molten electrolyte will remain below 1%. Nevertheless, if the process is carried out in such a manner that there is contact between the molten electrolyte and the gaseous titanium tetrachloride, then it is also possible to start the electrolytic reduction and the formation of the reducing agent with such low potential that from the beginning lower titanium chlorides of metallic titanium will be deposited on the cathode and, in such case, it is not necessary to start the process at the higher cathode potential which would be required for depositing alkali or alkaline earth metals on the cathode. However, and particularly in view of the low solubility of titanium tetrachloride in the molten electrolyte, it is frequently advantageous to start the process with a higher cathode potential so that initially alkali or alkaline earth metal will be deposited on the cathode and will be used as the reducing agent for reducing gaseous titanium tetrachloride.

After the reaction between the reducing agent and gaseous titanium tetrachloride which takes place during the second phase of the process has been fully or partially completed, contact between the gaseous tetrachloride and the cathode member is interrupted and the cathode member is again immersed in the molten electrolyte and thereby subjected to the cathode potential which had been interrupted while the efiective portion of the cathode was in contact with gaseous titanium tetrachloride or with a mixture of the same with an indifierent gas such as argon. The product of the reduction of the gaseous titanium tetrachloride, i.e. lower titanium tetra-- chlorides are thereby introduced into the molten electrolyte and, in View of operation of the electrolytic cell, may be at least partially transformed into the reducing agent such as titanium dichloride or titanium metal whichjin the next following second phase will again react with gaseous titanium tetrachloride. Repetition of this two phase process will thus 'lead to an enrichment of the molten electrolyte with titanium dichloride and particularly titanium trichloride.

The end product obtained in this manner will consist of a molten electrolyte containing lower reduction products of titanium tetrachloride such as titanium dichloride and titanium trichloride. These lower chlorides may be separated from the molten electrolyte by fractional crystallization and filtration.

However, it is also possible to carry out the above described process in such a manner that as final product titanium metal is obtained. Preferably, this is accomplished by introducing into the electrolytic cell another cathode in addition to the above described cathode member which is alternatingly brought in contact with the molten electrolyte and with the gaseous titanium tetrachloride. This other cathode, in contrast to the cathode member described further above, will remain permanently in the molten electrolyte and will serve for the precipitation of titanium metal thereon. Optimum conditions for the deposition of titanium metal may be arranged by separating the molten bath in the electrolytic cell into a portion in which the movable cathode member is located and into another portion in which the stationary cathode is arranged on which the titanium metal will be deposited. Here again it is possible to arrange the speed of the various reactions so that the amount of lower titanium chlorides which is introduced into the molten electrolyte by the movable cathode member which previously has been in contact with gaseous titanium tetrachloride, is commensurated to the amount of titanium metal which is deposited on the stationary cathode. In this manner, the concentration of titanium chloride in the molten elec trolyte can be kept at a constant level. in other words, the process is preferably carried out in such a manner that per unit of time, a quantity of titanium compounds originating from the gaseous titanium tetrachloride is deposited on the movable cathode member which corresponds to the quantity of titanium metal which is simultaneously deposited at the stationary cathode whereby, however, due to the high speed of the reaction at the movable cathode member and due to the high concentration of titanium ions at or in the Vicinity of the stationary cathode, the speed of recovery or production of titanium metal will be much greater than the speed with which titanium metal can be recovered from solutions of titanium tetrachloride in the customary molten electrolyte mixtures and at the customary temperatures such as 500 to 890 C. of the electrolysis of titanium tetrachloride dissolved in the molten electrolyte.

The titanium metal is deposited at the stationary cathode in relatively loose form and can be easily recovered by being scraped off the cathode or, however, it is also possible to use as material for the stationary cathode a thin titanium metal sheet which is replaced when its thickness has sufficiently increased due to the deposition of metallic titanium.

It is also possible and within the scope of the present invention to form on the cathode which alternatingly is located in the electrolytic cell and in the titanium tetrachloride containing gas space, a layer of titanium metal which will serve as reducing agent when the cathode is in contact with a gaseous titanium tetrachloride. This can be furthermore arranged so that contact between the cathode and the gaseous titanium tetrachloride is interrupted prior to the point at which all of the titanium metal deposited on the cathode would have reacted with the titanium tetrachloride. in this manner, the movable cathode can serve to form and transfer lower titanium chlorides into the molten electrolyte while simultaneously forming a metallic titanium layer of increasing thickness on such cathode. Once optimum concentration of lower titanium chlorides in the molten electrolyte has been reached, this process can be so controlled that such concentration of lower titanium chlorides in the molten electrolyte will remain substantially constant.

The reducing agent which is deposited at the cathode member during operation of the electrolytic cell may consist of at least one of the alkali or alkaline earth metals or of titanium metal or titanium dichloride, whereby deposition of alkali or alkaline earth metals is usually limited to the initial stage of the operation, and is terminated in favor of deposition of titanium metal or titanium dichloride as soon as the concentration of titanium chlorides in the molten electrolyte has risen to a desired level. The choice of the specific reducing agent which will be deposited at the cathode is controlled by adjustment of the cathode potential.

The melting points of the alkali and alkaline earth chlorides will to a considerable extent determine the temperature of the molten bath of electrolyte. Broadly, the more frequently used alkali and alkaline earth metal chlorides possess melting points which range from 606 C. for lithium chloride up to 960 C. for barium chloride. Various mixtures of the alkali and alkaline earth metal chloride give particularly good results and to some extent, the best mixture for any given operation will depend on the variables of the process. Particularly good results have been obtained by using as electrolyte a mixture of 32 molar percent of potassium chloride and 58 molar percent of lithium chloride. The melting point of this mixture is at about 400 C. The temperature of the electrolyte during the electrolysis will be 500-600 C., so that thereby it is not to be feared that the mentioned chlorides will be separated or precipitated in the molten bath in the solid form. When it is desired to produce metallic titanium either on the cathode which is alternatingly in contact with the electrolyte and the gaseous titanium tetrachloride, or preferably on a cathode which is continuously in contact with the bath of molten electrolyte, then the optimum concentration of titanium dichloride or trichloride in the molten electrolyte will be lower than when the desired end product consists of titanium dichloride or trichloride which is to be separated from the molten electrolyte by fractional crystallization.

For the precipitation of metallic titanium, only the concentration of the lower titanium chlorides which are actually dissolved in the molten electrolyte will be of importance. Increasing the concentration of the lower titanium chlorides in the molten electrolyte above their solubility so that a suspension of lower titanium chlorides in the molten electrolyte is formed, will interfere with the deposition of metallic titanium at the cathode. This is the reason why the concentration of lower titanium chlorides in the molten electrolyte is kept at a relatively low level, below the level at which crystallization of lower titanium chlorides will take place, when it is desired to form metallic titanium at the cathode. For instance, in a eutetic lithium chloride-potassium chloride melt having a temperature of between 500 and 600 C., the concentration of titanium trichloride will be kept at below 20% by weight.

On the other hand, when it is desired to recover titanium chlorides, then the introduction of lower titanium chlorides which are carried into the molten electrolyte by the cathode which previously has been in contact with gaseous titanium tetrachloride, is continued until the solubility of such lower titanium chloride in the molten electrolyte is exceeded and the lower titanium chlorides separate in the form of a suspension in the molten electrolyte.

Titanium tetrachloride can be reduced with titanium metal or also with titanium dichloride. Thus, when there is an excess of titanium tetrachloride, the end product of the reduction process, irrespective of whether titanium metal or titanium dichloride is used as the reducing agent, will be titanium trichloride. In other words, if the cathode during the second phase of the process is allowed to remain in contact with gaseous titanium tetrachloride for a sufiicient length of time, primarily titanium trichloride will be formed. However, if the reducing agent consists of titanium metal orparticularly during the starting periodof an alkali or alkaline earth metal, and if the time of contact between the reducing agent and the gaseous titanium tetrachloride is shortened, than primarily titanium dichloride rather than titanium trichloride will be formed. In addition, titanium dichloride is also produced during the first phase of the process, namely during operation of the electrolytic cell, from titanium trichloride which has been deposited on the cathode while the same was in contact with gaseous titanium tetrachloride and which subsequently has been introduced into the molten electrolyte. Such titanium dichloride produced during the electrolytic process is an intermediate during the reduction to metallic titanium, and it is also formed by reaction of electrolytically produced titanium metal with titanium trichloride present in the molten electrolyte.

At least theoretically, it would appear possible to carry out the present process without the use of an electrolyte preferably consisting of chlorides of alkali and alkaline earth metals. In other words, it would appear possible to subject molten lower titanium chlorides to electrolysis so as to either reduce titanium trichloride to titanium dichloride or to continue reduction until metallic titanium is formed. However, the lower titanium chlorides have a relatively high melting point and are of poor conductivity. Furthermore, sublimation for instance in the case of titanium trichloride and decomposition of molten electrolyte consisting exclusively of lower titanium chlorides would create considerable difficulties. Consequently and for all practical purposes, it appears preferable to carry out the electrolytic reduction of titanium chlorides, particularly lower titanium chlorides, during the first phase of the process in such a manner that the titanium chlorides are present in solution in a suitable molten carrier such as the chlorides of alkali and alkaline earth metals and mixtures of the same.

It is the important function of the alkali and alkaline earth metal chlorides as solvents for the lower titanium chlorides during electrolytic reduction of the latter, that the electric conductivity of the molten mass is greatly increased by the alkali and alkaline earth metal chlorides.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which FIGS. 1-7 are schematic illustrations of preferred embodiments of the apparatus according to the present invention.

As can be seen from the drawings, several preferred embodiments are within the scope of the present invention. The apparatus includes the conventional elements of electrolytic devices such as a container or space for holding the electrolyte, cathodes and anodes, as well as diaphragm means for separating the anode space from the cathode space. The cathodes according to the resent invention are cathode members which alternatingly can be brought in contact with the molten electrolyte and the gaseous titanium tetrachloride, as well as cathodes which serve for precipitation 'of titanium metal thereon and for subsequent removal or recovery of the titanium metal. One and the same anode or anodes may coast with both types of cathodes. Reduction products of titanium tetrachloride are precipitated at the cathodes, while at the anode which continuously remains in contact with the bath of molten electrolyte, chlorine is freed. The chlorine gas is then removed in suitable manner. The cathode members may be brought in contact with the bath of molten electrolyte and alternatingly therewith with the titanium tetrachloride containing gas space by various means. For instance for periodic alternating contacting of molten electrolyte and the gas space, the cathode may be moved in a reciprocating manner between the electrolyte space and the titanium tetrachloride containing gas space, whereby the length of time for which the cathode member is in contact with the gasspace or the molten electrolyte can be controlled in any desired manner. However, it is also possible to arrange stationary cathode members and to pass molten electrolyte alternatingly with titanium tetrachloride vapors over the same. Here again, the time periods for which the cathode is exposed to either the molten electrolyte or the titanium tetrachloride vapors can be controlled and need not necessarily be the same. Preferably, several cathode members are arranged within one device and the operating phases of the individual cathode members are staggered so that at any time at least one of the cathode members actually acts as cathode in the electrolytic cell and so that the current load of the cell remains relatively constant.

At least one anode will be arranged. cooperating with the above described cathode members as well as with the separate cathodes which serve for precipitation of titanium metal and subsequent recovery thereof. The area around the anode which contains the anolyte will be suitably closed off and provided with conduits for the withdrawal of the freed chlorine gas. In order to obtain the desired high current yield, a semi-permeable wall such as a diaphragm will be arranged so as to separate the the cathodic electrolyte area from the anodic electrolyte area.

Movement such as reciprocal movement of the cathode members can be accomplished in various ways, for in stance by suspending the cathode in a cathode area the upper portion of which is filled with titanium tetrachloride vapors, while the lower portion of the cathode area forms part of the electrolytic cell and is filled with molten electrolyte. The cathode can then be mechanically moved for instance upwardly and downwardly, so that at spaced intervals the cathode will be immersed in the molten electrolyte and at the periods between these spaced intervals the cathode will be in contact with gaseous titanium tetrachloride. The cathode carrier member will then have to pass through the wall of the device in a gas-tightly sealed manner and the movement of the cathode can :be actuated by means known in the art, preferably pneumatically. It is also possible to interpose a pneumatically actuated resilient means such as a spring which is located adjacent to the cathode area and communicating with the same and which is closed otf against the outer atmosphere and maintained at low temperature, whereby a movement of the spring and thus of the cathode can be effected and controlled by compressed gas.

According to another preferred embodiment, the cathode member which alternatingly will be in contact with the molten electrolyte and with gaseous titanium tetrachloride can be formed as a disc arranged on a current conducting rotatable shaft which passes in a fluid-tight manner through the outer wall of the device. The lower portion of the cathode disc will be immersed in the molten electrolyte while the upper portion of the disc will be in contact with gaseous titanium tetrachloride. Upon rotating of the shaft and thus of the cathode disc, portions of the disc which were immersed in the molten electrolyte and on which reducing agent has been deposited, will reach the gas space wherein the reducing agent will react with gaseous titanium tetrachloride thereby forming reduction products of titanium tetrachloride which upon further turning of the disc will be introduced into the molten electrolyte. Specific operating conditions can be controlled by the number of rotations of the shaft per unit of time and by adjustment of the depth to which the disc will be immersed in the molten electrolyte. The cathode member may also be formed by the outer or inner or both faces of a rotatable cylindrical wall, whereby speed of rotation about the axis of the cylinder and depths of unmersion of the cylindrical wall in the molten electrolyte Will control the time periods of immersion in the electrolyte and exposure to gaseous titanium tetrachloride relative to each other. The main difference between the disc and the cylindrical cathode is that the outer portions of the disc cathode move at a greater absolute speed than the portions thereof which are closer to the center of the disc, While in contrast thereto all portions of'the inner or outer cylindrical wall will move with equal speed.

In larger industrial devices in accordance with the present invention it has been found advantageous to arrange stationary cathode members in series in the legs of a tubular cathode space of U-shaped or V-shaped tubular cross section, whereby controlled pulsating movement of molten electrolyte and gaseous titanium tetrachloride will bring the cathode alternatingly in contact with the electrolyte and the gas. Or, two rows of cathode members can be stationarily installed in an electrolyte container, or in the cathodic area thereof, and the entire container or the cathodic portion thereof can be moved in a rocking member such as sometimes employed in crystallizing devices, so that during such rocking of the electrolyte containing container alternatingly one or the other series of cathode members will be immersed in the electrolyte or will be located in the titanium tetrachloride containing gas space. In this last described embodiment, preferably, the anodes are located in between the two rows of cathode members and are surrounded by tubular members which at their open end are closed by a suitable diaphragm, in such a manner that the anodes, being located in the center of the rocking device will at all times be immersed in the molten electrolyte.

Furthermore, the cathode members may be formed of graphite and so as to have relatively large surface areas which periodically during the second phase of the process are freed from electrolyte by a strong current of gaseous titanium tetrachloride which is directed against the cathode surfaces. Thereby, shape and inclination of the cathode surface, including the arrangement of grooves and the like thereon will improve the blowing off of electrolyte which might have been carried along during movement of the cathode from the molten electrolyte into the gas space.

When it is desired to produce metallic titanium, the final separation of the metal can be carried out in a second or auxiliary electrolytic cell with cathodic electrolyte circulating between the above described primary electrolytic cell and the auxiliary electrolytic cell, so that equalization of the concentration of lower titanium chlorides in the electrolyte is maintained. Thereby, movement of the molten electrolyte can be actuated by providing for a sufficiently great temperature differential between the first and second electrolytic cell or cell portions so that a thermosyphon effect will be accomplished. In connection with the last discussed embodiment, it has been found advantageous to interpose in the flow of the molten electrolyte a filtering device so that during each circulation of the electrolyte through the cell system, the electrolyte will be freed from suspended impurities which otherwise might interfere with the precipitation of the titanium metal.

Furthermore, when it is desired to obtain metallic titanium, the electrolytic cell arrangement may be provided with an upper portion into which the titanium metal carrying cathode can be moved without contact with the outer atmosphere and wherein the cathode and the titanium metal thereon can be cooled in a protective gas atmosphere such as an argon atmosphere and subsequently the titanium metal can be removed from the cathode.

The walls which separate and connect the cathodic and anodic spaces of the cell can be formed as diaphragms for instance of fritted glass, or of a loose sufliciently finely granulated mass of ceramic or carbon containing material, for instance graphitic material which is resistant against attack by the molten electrolyte.

The drawings will now be described in connection with the following examples, the invention however not being limited to the specific details of either the drawings or the examples.

EXAMPLE 1 Referring to FIG. 1 of the drawing, it will be seen that electrolyte J consisting of an approximately eutectic lithium chloride-potassium chloride melt, is located in a cylindrical beaker B and is maintained therein at a temperature of about 600 C. Tubular member C is arranged coaxial with and partially inside beaker B. Cathode members K and K are located in tubular member C. The lower end of tubular member C is closed by diaphragm D consisting of fritted glass. A third cathode, K is also located in tubular member C and will remain permanently immersed in liquid electrolyte I which fills the lower portion of tubular member C. In case that metallic titanium shall be produced as final product, the cathode K and the anode A should be connected with a separate electric circuit, when the lower titanium chlorides have attained the required concentration.

Tubular member or cathodic insert C is closed at its upper end by a stopper through which electric conduits E lead to cathodes K K and K and through which various conduits pass namely conduit F for introduction of titanium tetrachloride, conduit G for introduction of argon and conduit H for withdrawal of titanium tetrachloride and argon. The electric conduits E leading to cathodes K and K are movable in upward and downward direction without however allowing for the passage of fluid through the stopper closing the upper end of tube C. Cathodes K and K are made of graphite and formed with grooves which facilitate adherence of the reducing agent to the respective cathode. A graphite rod A serves as anode. Preferably separate circuits are formed including, respectively, an anode and one of the three cathodes. Chlorine gas formed at the anodes is removed through conduit L.

In the above described device, for instance, cathode K will be immersed in molten electrolyte J and at the beginning of the electrolytic process a thin layer of lithium will be precipitated on the surface of cathode K The area above the molten electrolyte and within tube C is filled with titanium tetrachloride. Upon upward moVement of cathode K the same will come in contact with gaseous titanium tetrachloride and this will result in immediate reaction forming titanium trichloride and titanium dichloride at the surface of upwardly moved cathode K Upon subsequent downward movement of cathode K and immersion of the same with the lower titanium chlorides thereon in the molten electrolyte, the lower titanium chloride will be dissolved in the electrolyte while again lithium will be precipitated on the cathode. This process in which the cathode will alternatingly remain for a short period of a few minutes or less in the molten electrolyte and in the gas space,is now repeated and will lead to an increase in the concentration of titanium trichloride and titanium dichloride in the molten electrolyte. Cathode K is operated in a similar manner, however staggered relative to cathode K so that one of the electrodes will be at all times immersed in the electrolyte and thus closing the electric circuit.

By operating the above described device in such a manner that each of the two cathodes K and K will remain for five minutes immersed in the electrolyte and then for five minutes exposed to the gas space, and with a current of between 1 and 1.5 amperes and a voltage of 5 volts at the start of the operation and 3.5 volts during the later part of the process, a continuing increase in the titanium chloride content of the molten electrolyte can be observed such as is shown in the following table.

s,os7,112

During the first hour while the voltage is maintained at 5 volts, the reducing agent produced during operation of the electrolytic cell consists primarily of lithium, after 1 hour the voltage is reduced 3.5 volts and titanium is deposited on the cathodes while the same are immersed in the molten electrolyte, and continuously on stationary cathode K The initial precipitation of the alkali metal speeds up the increase in concentration of the lower titanium chlorides, however, a certain disadvantage is connected with precipitating lithium, namely that precipitated lithium which forms a colloidal solution in the electrolyte, will cause an undesirable precipitation of finely sub-divided titanium metal in the molten electrolyte.

Once the concentration of titanium trichloride in the molten electrolyte starts to exceed 20%, the molten mass within cathode tube C will become more and more viscous due to the precipitation and suspension of titanium trichloride crystals.

Melts containing the high concentrations of lower titanium chlorides, particularly titanium trichloride can be easily worked up for the purpose of isolating titanium trichloride, so that in this case the method described therein can be considered as an electrolytic method of producing titanium trichloride from gaseous titanium tetrachloride.

The quantitative relationship between titanium trichloride and titanium dichloride can be adjusted by a suitable control of the relative length of time for which the cathodes are in contact with either the molten electrolyte or the gaseous titanium tetrachloride.

When it is desired to operate as described herein for the purpose of producing metallic titanium, then it is generally not required to reach such high concentration of lower titanium chlorides as are described in the table. These concentrations go considerably above the limit of solubility of titanium dichloride and titanium trichloride in eutectic lithium and potassium chloride mixtures, so that considerable portion of the lower chlorides will be present in the form of solid particles suspended in the molten electrolyte.

EXAMPLE 2 This example will refer to FIG. 2 of the drawing. Electrolyte containing vessel B is closed at its upper end with a stopper holding the following devices: A cathode tube C containing a cathode K which is fixed during the electrolysing period, and which can be removed after titanium metal has been produced by connecting the oathode K and the anode A with a separate electric circuit. A cathode tube C extends upwardly for a considerable distance above the upper end of container B. The upper portion G of this tube C is formed as a lock or a sluice, e.g. in the form of a slide for the gas-tight introducing and removal of the cathode K under a protective gas such as argon, after suitable lowering of its temperature. The outer electrolyte area outside of tube C holds several cathodes K which may be moved from a position below the level of the molten electrolyte to a position above the level of the molten electrolyte and within the gas space containing titanium tetrachloride. Furthermore, anodes A are located in the outer space of electrolyte container B and are surrounded by cylindrical tubes. The number of electrodes is greater than the number actually illustrated in H6. 2. Cathode K which corresponds to cathode K of FIG. 1 is pneumatically actuated so as to move between a lower and an upper position. This is done in order to avoid the necessity of forming a gas-tight passage for the actuating member of cathode K through the cover of container B. Actuation of cathode K is carried out by subjecting resilient body F located in an extension of the titanium tetrachloride containing gas space, in such a manner that resilient body P will not be subjected to direct attack by the molten electrolyte but need only be resistant against the titanium tetrachloride vapors. Space G communicates with the interior of vessel 3. However, space G is maintained at such low temperature that the elasticity of resilient hollow body F will not be impaired, although the temperature will be higher than the boiling point of titanium tetrachloride, i.e. at least 137 C. Upward and downward movement of cathode K is actuated by the periodical introduction of gas under pressure through conduit E in the interior of resilient body F. It is desirable to keep the distance of the upward and downward movement of cathode K to a minimum and thus, it is preferred to increase the surface'area of the same by forming the cathode as a grating rather than obtaining the same surface area by having a sheet-like cathode which would have to be of much larger dimensions.

Anode A is formed of a graphite rod and is surrounded by tubular member M through which chlorine gas developed at anode A passes to conduit L. Tubular member M is closed at its lower end by diaphragm D which in the illustrated embodiment consists of a layer of particulate material which must be resistant against all corrosive attacks to which it may be exposed in the molten electrolyte. Tubular member M is embedded sufiiciently deep in diaphragm mass D to obtain the desired conditions with respect to conductivity and reduction of convective and diifusion-caused losses.

Gas pressure impacts which are conveyed via opening E to the interior of resilient body F will move cathode memberK during space periods of high pressure, down- Wardly into the liquid electrolyte bath while during periods of release of gas pressure, the resilient body F will contract causing upward movement of cathode member K Resilient body F may, for instance, consist of a cylinder made of thin corrugated steel sheets.

The cathode may be formed as a grating, i.e. of a plurality of sheets arranged parallel to each other so that immersion of the cathode in the molten electrolyte for a relatively small distance will already expose a relatively large cathode area to contact with the electrolyte.

EXAMPLE 3 The present example relates to the embodiment illustrated in FIG. 3. As can be seen, the cathode is formed as a rotating disc which continuously or discontinuously moves through the molten electrolyte and through the titanium tetrachloride filled gas space above the molten electrolyte. The number of turns of the disc per unit or time and the depths to which the disc is immersed in the molten electrolyte will control the relationship be tween the electrolytic phase and the phase in which the disc is in contact with gaseous titanium tetrachloride. Both phases occur simultaneously and on one and the same disc-shaped cathode. Thus, the disc of the embodiment of FIG. 3, as well as the cylinder of the embodiment of FIG. 4 represent a plurality of the cathodes K and K of PEG. 1, of which each during each complete turn passes through phases 1 and 2 of the process.

Indicia B indicates the container for the electrolyte which may for instance be a cylindrical container heated from outside. Shaft N passes through the wall of container B and rests in fluid-tight bearings. Shaft N and disc cathodes K and K mounted thereon turn at'a predetermined speed so that, as illustrated, at any given time a major portion of disc cathodes K and K will be located in the gas space in contact with gaseous titanium tetrachloride and a smaller portion of the surface of discs K and K will be immersed in the molten electrolyte. The upper level of molten electrolyte J is indicated by line 0. Anodes A are arranged in a manner somewhat similar to the embodiment illustrated in FIGS. 1 and 2 laterally spaced from shaft N. The portion of the electrolyte 3 adjacent to anodes A is separated from the catholyte in conventional manner by diaphragm D which may be either of the type described in connection with FIG. 1 or of'the type described in connection with FIG. 2. Chlorine formed at anodes A 13 is thus kept'within tubular members M and is withdrawn through conduits L.

The upwardly elongated tubular portion C serves for withdrawal of cathode K without exposing K to the outer atmosphere, and for introduction and withdrawal of titanium tetrachloride as well as of inert protective gas such as argon. FIG. 3 will also serve to indicate an arrangement whereby cathodes K and K are replaced by cylindrical cathodes coaxial with shaft N. The walls P of such cylindrical cathodes are indicated in FIG. 3 in broken lines. As previously stated, it is an advantage of an arrangement including the cylindrical cathodes P as compared with disc cathodes K and K of FIG. 3, that cylindrical cathodes P will move with equal circumferential speed throughout. Such equal speed at all points of the cathode will lead to the formation of an even electrolyte film and thus to equal conditions at all portions of the surface during phase 2 of the process, i.e. during the phase in which the reducing agent on the cathode reacts with gaseous titanium tetrachloride.

EXAMPLE 4 According to the embodiment described in the present and some of the following examples, the cathode member remains stationary and molten electrolyte is brought in contact with the cathode member alternatingly with gaseous titanium tetrachloride.

As shown in FIG. 4, cathode member K is in the shape of a cylinder open at its lower end and at the outside of its lower portion protected by an insulating tube Q. The upper end of the tubular cathode member K is closed as indicated by cross hatching. Gaseous titanium tetrachloride is introduced through tubular member C. During the electrolytic phase or phase 1 of the process, the bell-shaped portion of cathode member K which is immersed in molten electrolyte will be completely filled by the same. The second phase of the process, i.e. the phase in which reducing agent formed on cathode member K reacts with titanium tetrachloride vapors, is introduced by passing titanium tetrachloride vapors under pressure through conduits G and C into the bell-shaped portion of cathode member K i.e. under sufiicient overpressure so as to push the electrolyte from the interior portion of cathode K Thus, the reducing agent formed in the first phase of the process on the interior wall of the widened bell-shaped portion of cylindrical cathode member K will now come in contact with gaseous titanium tetrachloride and will cause reduction of the latter. The

pulsating introduction of titanium tetrachloride vapors under pressure can for instance be carried out in an easily and automatically controllable manner by evaporating at spaced intervals a quantity of liquid titanium tetrachloride located in tube C, which quantity upon evaporation will form the gas volume required for producing the necessary overpressure for pushing molten electrolyte downwardly out of the widened lower portion of cathode member K The corresponding reduction of pressure in order to again introduce molten electrolyte into the lower portion of the cathode member K can be easily carried out by actuating a cooling device adapted to condense titanium tetrachloride vapors. Such cooling device (not shown) is to be arranged so as to communicate with tube C. However, it is also within the scope of the present invention to create the pulsating titanium tetrachloride vapor pressure by any other means known in the art.

Electrolyte which is pushed out of the interior of cathode member K by the overpressure of titanium tetrachloride vapors, will rise in the annular portion defined between the tubular wall R which limits the cathode space and the insulating wall Q on the outer face of the lower portion of cathode member K Anodes A are arranged in the cell outwardly of wall R and the anolyte is separated from the catholyte by diaphragm D which is illustrated in FIG. 4 as consisting of a layer of particulate material which is not attacked by the molten electrolyte and into which penetrates the lower portion of cylindrical wall R. Such particulate diaphragm material may consist of particles of ceramic material, quartz, glass of high melting point or graphite and generally will have a particle size of between 0.1 and 1 millimeter in order to achieve the desired diaphragm effect, whereby the height of the layer of diaphragm forming particles, the diffusion losses and voltage losses caused by the diaphragm must be considered. Such diaphragm layer as well as diaphragm which for instance consist of fritted glass, as well as a manner of application of the same are well known in the art.

For large scale operation, a plurality of individual relatively small bell-shaped cathode members such as i1- lustrated in FIG. 4, are arranged side by side and/or also vertically spaced from each other, whereby anodes with suitable means for removal of chlorine gas are arranged around and between the individual cathode members.

EXAMPLE 5 FIG. 5 illustrates another embodiment of the present invention according to which the electrodes are stationary and molten electrolyte alternates with gaseous titanium tetrachloride in contacting cathode members K and K The cathode members K and K are arranged, respectively, in the legs of a U-shaped vessel and the level of molten electrolyte in the legs of the U-shaped vessel will alternatingly and reciprocally rise and fall. Thus, as illustrated, molten electrolyte covers the cathode member K while the level of molten electrolyte J is below cathode member K Movement of the molten electrolyte is easily accomplished and controlled by al ternatingly introducing gas under pressure, for instance titanium tetrachloride, into the respective legs of the U-shaped vessel. Cathode K serves for accumulation of titanium metal and means are provided for withdrawing cathode K under a protective gas atmosphere so that the titanium metal accumulated thereon can be removed. The arrangement of anodes A and cathode K is substantially the same as described in connection with other embodiments of the present invention. The illustration of the device in FIG. 5 is of a schematic nature and it is of course within the scope of the present invention to increase the number of legs or to make other suitable changes in the device which then still will operate essentially in the manner described in the present example.

EXAMPLE 6 The alternating immersion and freeing of stationary cathode members K and K from molten electrolyte can also be accomplished for instance in a device similar to that illustrated in FIG. 5, but without causing movement of the molten electrolyte by pulsating introduction of gaseous pressure. It is for instance possible to mount the apparatus of FIG. 5 on a vertical disc and then to turn the disc about its axis to one or the other side, whereby, when the disc is turned in the direction toward cathode member K the level of molten electrolyte in the legs of the apparatus containing member K will rise and the level of the molten electrolyte in the other leg of the apparatus will fall correspondingly. Thus, in this manner, cathode member K will be immersed in the molten electrolyte and simultaneously cathode member K will be exposed to gaseous titanium tetrachloride. This is then reversed by turning the disc in opposite direction, i.e. in the direction toward cathode member K This arrangement has some similarity with the cradle devices sometimes used in connection with crystallizing dishes. Cathode K and anode A are arranged in the center portion of the device so that their position relative to the surrounding molten electrolyte will not be changed by the pulsating change in the upper level of molten electrolyte in the two legs of the apparatus.

EXAMPLE 7 The present example relates to FIG. 6 of the drawing, according to which titanium tetrachloride gas is periodically brought in contact with the cathode thereby displacing the molten electrolyte which covers the cathode during intervening periods. This is accomplished according to the present example by suddenly blowing a high pressure or high velocity stream of gaseous titanium tetrachloride against cathode member K Cathode member K may be formed with a grooved or ribbed surface which will assist in distributing the stream of gas over the entire surface of cathode member K and in displacing electrolyte adhering thereto. Displacement of electrolyte is facilitated by a substantially upright or only slightly inclined position of the cathode sheet, while a horizontal arrangement of the cathode is not recommended.

In FIG. 6 B represents a heatable cell container, the center portion of which is occupied by cathode vessel T while the anodes A are arranged in compartments outside of inner vessel T. Communication and separation between anode and cathode space is provided by diaphragm D. Titanium tetrachloride is blown through the holes of pipe S against cathode member K which is immersed in molten electrolyte. During the spaced time periods during which titanium tetrachloride vapors are thus blown against cathode member K the molten electrolyte will be blown away from the surface of cathode member K and thus reduction of titanium tetrachloride in contact with the reducing agent formed on the surface of cathode K during the first phase or electrolytic phase of the process can take place.

EXAMPLE 8 Since the optimum conditions for increasing the concentration of lower titanium chloride in the molten electrolyte are frequently different from those for the final separation of titanium metal with respect to temperature, movement and purity of the electrolyte, materials best suitable for the contacting portions of the apparatus, etc. it is also contemplated to carry out the process of the present invention including the separation of titanium metal in an apparatus in which the separation of the metal is spaced from the portion of the apparatus in which enrichment of the electrolyte with lower titanium chlo rides takes place. This is illustrated in FIG. 7 of the drawing. It can readily be seen that the separate vessel in which titanium metal is recovered forms part of the electrolytic cell, however, nevertheless is separated in such a manner that the electrolyte which circulates between the two portions of the electrolytic cell can be adjusted to optimum conditions required in each of the two portions.

Since the circulating speed of the electrolyte, which is required according to the present embodiment, is relatively slow, it is frequently possible to use for such circulation a thermosyphon efiect caused by the temperature differential of electrolyte in vessels A and M. In most cases, such thermosyphon effect will be suflicient to cause circulation of the molten electrolyte even when the electrolyte while passing from vessel A to vessel M is subjected to filtration. In cases where the temperature difference does not suffice to cause the desired circulating movement of the electrolyte, forced movement by conventional means such as pump means must be arranged.

Separation of the metal recovery from the portion of the electrolytic apparatus in which enrichment of the electrolyte with lower titanium chlorides takes place, will have several advantages particularly with respect to the gas trap arrangement required for removal of the separated metal from the apparatus and, furthermore, will allow to operate at higher temperature in the portion of the apparatus in which titanium metal is separated.

Preferably, separate anodes will be provided for porl6 tions A and M of the apparatus so that the only connecing feature will be the circulating electrolyte.

Referring now again to FIG. 7 of the drawing, it will be seen that electrolytic cell A in which enrichment of the molten electrolyte with lower titanium chlorides takes place, communicates through conduit Z with electrolytic cell M in which separation of titanium metal takes place, so that molten electrolyte can flow from cell A to cell M and again back to cell A. Cells A and M may be maintained at a different temperature so that also the electrolyte in cells A and M will be of difierent temperature and thus the flow of electrolyte can be actuated by a thermosyphon effect. For this purpose, for instance heating elements H and also cooling elements K may be operatively arranged along conduit Z. It is of course also possible to maintain a forced circulation, for instance by means of pump P. Such forced circulation can also be effected by injection means, whereby either liquid electrolyte or an inert gas such as argon may be used as the injection fluid and introduced into one of the legs of conduit Z.

A continuous filtration of the electrolyte while passing from cell A to cell M will be carried out in filter element P which is interposed into conduit Z. Filter media which may be used for this purpose are well known in the art and generally consist of masses of particulate material similar to those which were described for the'purpose of forming diaphragm masses for separation of the anolyte from the catholyte. The purpose of such filtration prior to passage of the molten electrolyte into electrolytic cell M is the removal from the electrolyte of suspended material which might have an unfavorable effect on the crystallization of titanium metal in electrolytic cell M.

Basically, electrolytic cells A and M contain the same elements as that described in connection with drawings l-6 with the difference that reduction of titanium tetrachloride and enrichment of the molten electrolyte with lower chlorides of titanium takes place in cell A spaced from the further reduction to and separation of titanium metal which will take place in cell M. Cell A can be construed in accordance with any of the embodiments described further above. The apparatus according to the present example is schematically illustrated in FIG. 7 wherein the cathode K serves together with anode A for reduction of titanium tetrachloride and enrichment of the electrolyte with lower chlorides of titanium. Diaphragm D will separate the anolyte from the catholyte in cell A and suitable conduits for introduction of titanium tetrachloride and a protective gas such as argon, as well as for the removal of chlorine gas are provided. Electrolytic cell M includes a cathode K on which titanium metal is deposited and an anode A including diaphragm D and a conduit for removal of chlorine gas from the anode space. Again, a conduit is shown for the introduction of argon, and a trap device Sch'l including gate valve Schi for the removal of titanium metal-bearing cathode K under a protective gas atmosphere.

Many variations of the method and apparatus are within the scope of the present invention.

Thus, in the first or electrolytic phase of the process, a reducing agent for use in the second phase in which titanium tetrachloride is to be reduced, will be deposited on the cathode by electrolytic separation of a substantially or a completely chlorine-free material from the electrolyte. The reducing agent which will be electrolytically formed during the first phase of the process preferably will consist of either an alkali or alkaline earth metal, or of metallic titanium or titanium dichloride, whereby the separation of alkali or alkaline earth metal at the cathode is preferably limited to the initial period of the process in order thereby to speed up the increase in the concentration of lower titanium chlorides in the electrolyte. Once the concentration of lower titanium chlorides in the electrolyte has risen suiiiciently, it is preferred to deposit on the cathode either titanium or titanium dichloride as the 17 reducing agent. The specific material which will be deposited on the cathode can be controlled by adjustment of the cathode potential.

Frequently it is desired to produce in the above manner an electrolyte containing a concentration of lower titanium chlorides which is many times higher than the maximum concentration in which titanium tetrachloride could be dissolved in the electrolyte.

As has been described further above, it is also within the scope of the present invention to electrolytically separate on a spaced additional cathode titanium metal from the electrolyte which has been enriched with lower titanium chlorides. In this case, preferably the rate of enrichment of the electrolyte with lower titanium chlorides and the rate of separation of titanium metal are adjusted so that a substantially constant optimum concentration of lower titanium chlorides in the electrolyte is maintained. However, it is also possible to use one and the same cathode for separation of metallic titanium and for carrying out phases 1 and 2 of the process. This can be done for instance by depositing during the first phase of the process metallic titanium on the cathode and to use only a portion of the thus deposited metallic titanium during the second phase of the process for reduction of titanium tetrachloride. Preferably it is so adjusted that, once optimum concentration of lower titanium chlorides in the electrolyte is obtained, only as much titanium is used as reducing agent and thereby preferably transformed into titanium trichloride as is simultaneously deposited as metal on the cathode, so that concentration of the lower titanium chlorides in the molten electrolyte will remain substantially constant.

The materials which are used for the electrolytic cell and the entire apparatus according to the present invention are conventional material which must be resistant against the temperatures prevailing during the process, as well as against attack by the various substances and materials with which a portion of the device will come in contact. Thus, substantially all of the materials which are used in building electrolytic devices for the conventional decomposition of titanium tetrachloride with molten alkali chlorides, may be used. These materials include, besides ceramics, special glass, quartz, also graphite, stainless steel and titanium metal. The anodes on which chlorine gas will be developed are preferably made of graphite.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of devices for the reduction of titanium tetrachloride and the recovery of the thus formed reduction products differing from the types described above.

While the invention has been illustrated and described as embodied in an electrolytic device for the production of lower titanium chlorides and of titanium metal, it is not intended to be limited to the details shown, since various modification and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of reducing gaseous titanium tetrachloride and recovering the products formed by reduction of said titanium tetrachloride, comprising the steps of forming a liquid bath consisting essentially of a solution of a titanium chloride in at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, said material and said titanium chloride being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride; subjecting said bath to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a layer of said substance; withdrawing said member with said layer of said substance thereon from said bath; subjecting said layer on said withdrawn member to reaction with gaseous titanium tetrachloride so as to form a reduction product of said titanium tetrachloride adhering to said member; immersing said member with said reduction product adhering thereto in said bath so as to dissolve said reduction product in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of withdrawing, subjecting and immersing of said member so as to continue the formation of lower titanium chlorides and the dissolutween said layer and gaseous titanium tetrachloride are carried out in a continuous manner.

3. A method of reducing gaseous titanium tetrachloride and recovering the products formed by reduction of said titanium tetrachloride, comprising the steps of forming a liquid bath consisting essentially of a solution of a titanium chloride in at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, said material and said titaniumtetrachloride being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride; subjecting said bath to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said memher a layer of said substance; withdrawing said member with said layer of said substance thereon from said bath; subjecting said layer on said withdrawn member to reaction with gaseous titanium tetrachloride so as to form as a reaction product of said layer and said gaseous titanium tetrachloride a lower titanium chloride adhering to said member; immersing said member with said reaction product adhering thereto in said bath so as to dissolve said reaction product in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of withdrawing, subjecting and immersing of said member so as to continue the formation of lower titanium chlorides and the dissolution of the same in said bath.

4. A method of reducing gaseous titanium tetrachloride and recovering the products formed by reduction of said titanium tetrachloride, comprising the steps of forming a liquid bath consisting essentially of a solution of a titanium chloride in at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, said material and said titanium tetrachloride being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride; subjecting said bath to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a layer of said substance; withdrawing said member with said layer of said substance thereon from said bath; subjecting said layer on said withdrawn member to reaction with gaseous titanium tetrachloride so as to form as a reaction product of said layer and said gaseous titanium tetrachloride a lower titanium chloride adhering to saidmember; immersing said member with said reaction product adhering thereto in said bath so as to dissolve said reaction product in said material and also to form again by electrolytic deposition a layer of said substance on said member; repeating said steps of Withdrawing, subjecting and immersing of said member so as to continue the formation of lower titanium chlorides and the dissolution of the same in said bath; and electrolytically reducing at least a portion of said reaction product to metallic titanium.

5. A method as defined in claim 2 wherein the electrolytic reduction of said bath is initially arranged in such a manner that a layer of substantially chlorine-free metal of said material is formed on said member; and wherein upon progressive enrichment of said bath with dissolved reduction product of titanium tetrachloride electrolytic reduction of said bath is arranged in such a manner that a layer of at least one substance selected from the group consisting of titanium and titanium dichloride is formed on said member.

6. A method as defined in claim 4 wherein in a given time period the quantity of titanium tetrachloride which is reduced by reaction with said layer is commensurate to the quantity of metallic titanium formed by electrolytic reduction of said reaction product, so that in Continuous operation of said method the concentration of titanium chlorides in said bath remains substantial- 1y constant.

7. A method of reducing gaseous titanium tetrachloride and recovering the products formed by reduction of said titanium tetrachloride, comprising the steps of contacting during spaced first phases a current conducting member with a liquid bath consisting essentially of a solution of a lower titanium chloride in at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, said bath during said first phases being subjected to electrolysis with said current conducting member acting as cathode; separating at least a portion of said current conducting member during second phases alternating with said first phases from said liquid bath and surrounding said member during at least part of said second phases with gaseous titanium tetrachloride, so that during the first phases electrolytic reduction of said bath will take place under formation on said member of a layer adapted to reduce gaseous titanium tetrachloride, and during second phases said layer will react with the surrounding titanium tetrachloride reducing the same and forming a layer of reduced titanium tetrachloride on said memher, said layer of reduced titanium tetrachloride being dissolved in said bath during the subsequent first phase.

8. A method of reducing titanium tetrachloride, comprising the steps of subjecting a liquid bath, consisting essentially of at least one material in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; withdrawing at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said withdrawn portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower titanium chloride adhering to said member; immersing said member, with said lower titanium chloride adhering thereto, in said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of withdrawing, contacting and immersing in the indicated sequence so as to increase thereby the concentration of lower titanium chlorides in said bath.

9. A method of reducing titanium tetrachloride, comprising the steps of subjecting a liquid bath, consisting essentially of at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substantially chlorine-free substance capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; Withdrawing at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said Withdrawn portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower titanium chloride adhering to said member; immersing said member, with said lower titanium chloride adhering thereto, in said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of withdrawing, contacting and immersing in the indicated sequence so as to increase thereby the concentration of lower titanium chlorides in said bath.

10. A method of reducing titanium tetrachloride, comprising the steps of subjecting a liquid bath, consisting essentially of at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, and also including at least one titanium chloride in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; withdrawing at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said withdrawn portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower titanium chloride adhering to said member; immersing said member, with said lower titanium chloride adhering thereto, in said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of Withdrawing, contacting and immersing in the indicated sequence so as to increase thereby the concentration of lower titanium chlorides in said bath.

11. A method of reducing titanium tetrachloride, comprising the steps of subjecting a liquid bath, consisting essentially of at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, and also including at least one titanium chloride in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substance selected from the group consisting of alkali metals, alkaline earth metals, titanium metal and titanium dichloride capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; withdrawing at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said withdrawn portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower ti- 21 tanium chloride adhering to said member; immersing said member, with said lower titanium chloride adhering thereto, in said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of withdrawing, contacting and immersing in the indicated sequence so as to increase thereby the concentration of lower titanium chlorides in said bath.

12. A method of reducing titanium tetrachloride, comprising the steps of subjecting a liquid bath consisting essentially of at least one material in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; withdrawing at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said withdrawn portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower titanium chloride adhering to said member; immersing said member, with said lower titanium chloride adhering thereto, in said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer or" said substance on said member; repeating said steps of withdrawing, contacting and immersing in the indicated sequence so as to increase thereby the concentration of lower titanium chlorides in said bath; and separating by electrolytic deposition metallic titanium from the thus formed solution of lower titanium chlorides in said material.

13. A method of reducing titanium tetrachloride, cornprising the steps of subjecting a liquid bath, consisting essentially of at least one material selected from the group consisting of the chlorides of alkali metals and alkaline earth metals, and also including at least one titanium chloride in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; withdrawing at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said withdrawn portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower titanium chloride adhering to said member; immersing said member, with said lower titanium chloride adhering thereto, in said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer of said substance on said member; repeating said steps of withdrawing, contacting and immersing in the indicated sequence so as to increase thereby the concentration of lower titanium chlorides in said bath; and separating by electrolytic deposition metallic titanium from the thus formed solution of lower titanium chlorides in said material.

14. A method according to claim 13 wherein said cathodically reduced layer consists essentially of metallic titanium and is formed at a rate corresponding to the rate of reduction of gaseous titanium tetrachloride so that the concentration of lower titanium chlorides in said bath will remain substantially constant.

15. A method according to claim 8 wherein upon reaching a desired concentration of lower titanium chlorides in said bath, metallic titanium is withdrawn from said bath by electrolytic deposition, at a rate substantially corresponding to the rate of formation of lower titanium chloride from said gaseous titanium chloride so that the concentration of lower titanium chlorides in said bath will remain substantially constant.

16. A method according to claim 15 wherein the electrolytic deposition of metallic titanium is carried out on a cathode spaced from said current conducting member.

17. A method according to claim 8 wherein said current conducting member acting as cathode is stationary and is contacted alternatingly with said liquid bath and said gaseous titanium tetrachloride.

18. A method of reducing titanium tetrachloride, comprising the steps of subjecting a liquid bath, consisting essentially of at least one material in which titanium chlorides are soluble with the solubility of lower titanium chlorides in said material being greater than the solubility of titanium tetrachloride therein and said material at least partly being adapted to be cathodically reduced so as to form a substance capable of reducing gaseous titanium tetrachloride, to electrolytic reduction between an anode and a current conducting member acting as cathode so as to form on said member a reducing layer of said substance; separating at least a portion of said member with said layer of said substance thereon from said bath; contacting said layer on said separated portion of said member with gaseous titanium tetrachloride so as to react said layer and said gaseous titanium tetrachloride under formation of a lower titanium chloride adhering to said member; contacting said member, with said lower titanium chloride adhering thereto, with said bath so as to dissolve said lower titanium chloride in said material and also to form again by electrolytic deposition a layer of said substance on said member; and repeating said steps of contacting at least a portion of said member, contacting said layer and immersing said member, in the indicated sequence, so as to increase thereby the concentration of lower titanium chlorides in said bath.

References Cited in the file of this patent UNITED STATES PATENTS 2,880,156 Benner et al Mar. 31, 1959 2,951,021 Di Pietro Aug. 30, 1960 2,975,111 Reimert et al. Mar. 14, 1961 

1.A METHOD OF REDUCING GASEOUS TITANIUM TETRACHLORIDE AND RECOVERING THE PRODDUCTS FORMED BY REDUCTION OF SAID TITANIUM TETRACHLORIDE, COMPRISING THE STEPS OF FORMING A LIQUID BATH CONSISTING ESSENTIALLY OF A SOLUTION OF A TITANIUM CHLORIDE IN AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF THE CHLORIDES OF ALKALI METALS AND ALKALINE EARTH METALS, SAID MATERIAL AND SAID TITANIUM CHLORIDE BEING ADAPTED TO BE CATHODICALLY REDUCED SO AS TO FORM A SUBSTANCE CAPABLE OF REDUCING GASEOUS TITANIUM TETRACHLORIDE; SUBJECTING SAID BATH TO ELECTROLYTIC REDUCTION BETWEEN AN ANODE AND A CURRENT CONDUCTING MEMBER ACTING AS CATHODE SO AS TO FORM ON SAID MEMBER A LAYER OF SAID SUBSTANCE; WITHDRAWING SAID MEMBER WITH SAID LAYER OF SAID SUBSTANCE THEREON FROM SAID BATH; SUBJECTING SAID LAYER ON SAID WITHDRAWN MEMBER TO REACTION WITH GASEOUS TITANIUM TETRACHLORIDE SO AS TO FORM A REDUCTION PRODUCT OF SAID TITANIUM TETRACHLORIDE ADHERING TO SAID MEMBER; IMMERSING SAID MEMBER WITH SAID REDUCTION PRODUCT ADHERING THERETO IN SAID BATH SO AS STO DISSOLVE SAID REDUCTION PRODUCT IN SAID MATERIAL AND ALSO TO FORM AGAIN BY ELECTROLYTIC DEPOSITION A LAYER OF SAID SUBSTANCE ON SAID MEMBER; AND REPEATING SAID STEPS OFWITHDRAWING, SUBJECTING AND IMMERSISNG OF SAID MEMBER SO AS TO CONTINUE THE FORMATION OF LOWER TITANIUM CHLORIDES AND THE DISSOLUTION OF THE SAME IN SAID BATH. 